1. Field of the Invention
This invention relates to an initialization processing system of an in-car microcomputer of an air conditioning amplifier unit, etc., for controlling a vehicle air conditioning system.
2. Description of the Related Art
A conventionally known initialization processing system of a random access memory (RAM) of an air conditioning amplifier unit having a battery backup memory for controlling a vehicle air conditioning system writes a password into the RAM of the air conditioning amplifier unit when an ignition switch is turned off and makes a password check to see if the password read when the ignition key was turned on matches the written password. If both the passwords match, the processing system does not clear the backup memory; if the passwords do not match, the processing system clears the backup memory and initializes the RAM at the battery off to on time.
Thus, the read password (no password because of battery off) does not match the written password at the first time when the ignition key is turned on after battery replacement, so that the RAM is initialized at the battery off to on time.
However, the conventional initialization processing system of an air conditioning amplifier unit does not write a password at the instantaneous battery off and on time, thus clears the backup memory although the battery is not just after replacement (causes so-called lost memory).
In contrast, a proposal is made for providing an external interrupt port, monitoring low voltage in interrupt service before a password check, and performing ignition off processing, thereby writing a password into RAM regardless of the instantaneous battery off and on time.
However, in the conventional initialization technique, if noise is entered in the external interrupt port at the wiring connection time, etc., because of battery replacement and signals similar to those for instantaneously turning on and off the ignition key are input due to the noise, an external interrupt is enabled by the on signal and a password is written by external interrupt service of the off signal. Thus, when the ignition key is first turned on after battery replacement, password OK is returned from a password check and initial values are not set at the battery off to on time, resulting in a so-called abnormal memory state in which the backup memory remains cleared, causing the later control to become abnormal.